Maybe I've misunderstood the OP, but I'm reading it a different way, possibly because it's the way I used to be in matchplay with friends too.
I used to feel that I didn't want to be responsible for them not having a good time, and if I battered them that'd be the case.
I bought a book about developing a 'killer instinct'. It more more about life in general but had a section on sports.
I read a few chapters then stopped and haven't picked it up again since, because a more apt title for the book could have been "how to be an arse and not care about anyone else".
I did pick up something from it though, and have adapted my attitude partly due to that and partly from conversations with others and stuff read on the internet.
Think about it more like you want them to be impressed with your game, and (this is the bit from the book) make them not look forward to playing you if you get drawn together in a club knockout. Not in a "don't want to spend time with you" sort of way, but a "don't fancy my chances against you" way.
If you're 4 up, try to get 5 up. If you're 5 down with 6 to play, they won't think they have the upper hand next time if you take them to 17 or 18.
The final straw for me was losing to a guy that thought he had no chance against me. He was right (or should have been), but I lost to him partly through trying to help him feel more positive (like he was my partner - I know I'm an idiot) and partly through me not trying to kill the match off as quickly as I could. ie. if I had a 6' putt for the win I'd be happy with 2 for the half, that sort of thing.
All I ended up doing was losing a match I should have won, and making the guy think I wasn't as good as he previously thought I was. Lose-lose.
Show them how good you are, that they want to avoid you in the matchplay draw, but that you're great to spend a few hours with on the course if they draw you in a medal.
Great post, I'm going to adopt this in an attempt to move away from quiet, unassuming, shy, introvert nature and man up a bit..